— Small doses of a flame retardant commonly added to furniture and baby products can trigger obesity, anxiety and developmental problems, according to the first independent study of a chemical promoted as safe by industry and government officials.

Baby rats whose mothers ate tiny amounts of the chemical, known as Firemaster 550, gained significantly more weight than others that weren't exposed, according to a presentation Tuesday at a scientific conference here. The chemical made the female offspring more anxious, prompted early puberty and caused abnormal reproductive cycles.

"This raises red flags about a widely used chemical that we know little about," said study co-author Heather Stapleton, a Duke University chemist. "What we do know is, it's common in house dust and that people, especially kids, are being exposed to it."

The Tribune's "Playing With Fire" investigation, published in May, documented how Firemaster 550 is among generations of flame retardants that the U.S. Environmental Protection Agency has allowed on the market without thoroughly assessing health risks.

The EPA now says it will conduct a risk assessment of two brominated compounds in the flame retardant next year, citing potential health hazards and widespread exposure from household products. The move could lead to tougher regulations and restrictions on the chemical; in the past, similar assessments have pressured manufacturers to phase out products completely.

Introduced in 2003, Firemaster 550 was portrayed as a chemical that would neither escape from treated products nor cause health problems. Scientists have since found the flame retardant's ingredients not only in household dust but in air around the Great Lakes and in wildlife around the world.

Until now, the only health studies of Firemaster 550 were two papers the chemical's manufacturer submitted to the EPA in 2008. Those studies found that high doses can lower animals' birth weight, alter female genitalia and cause skeletal malformations such as fused ribs and vertebrae.

The new research, which the authors described as a pilot study that will help direct future work, focused on low doses of the chemical — no more than 3 milligrams per kilogram of weight per day. By contrast, the earlier studies concluded that 50 milligrams per kilogram was the lowest dose where harmful effects were seen.

"We set out to find if there are effects at levels similar to what people are exposed to in the real world," said co-author Heather Patisaul, a North Carolina State University toxicologist.

Stapleton and Patisaul's findings concern researchers studying how industrial chemicals can disrupt the endocrine system by mimicking or blocking natural hormones during critical stages of development. Among other effects, the team found that Firemaster 550 altered levels of thyroid hormones.

Citing funding constraints, Patisaul acknowledged that the new study involved fewer animals than the company research did. She and Stapleton tested three pregnant females and their offspring per dosage, while the other studies involved 25 animals and offspring per dosage.

Chemtura, the Philadelphia-based company that makes Firemaster 550, said in a statement that it would work with the EPA to "realize the ultimate benefits of Firemaster 550."

The company said its own studies show "the relative risk associated with Firemaster 550 is extremely low, and it is far outweighed by the advantages of a product that provides lifesaving and injury-reducing fire prevention benefits to millions of consumers every day."

The new study is being submitted amid fierce debate about toxic chemicals and the state and federal laws that regulate them. Most furniture-makers add flame retardants to foam cushions to meet a flammability standard California adopted in 1975, but some of the most widely used chemicals are linked to cancer, neurological deficits, developmental problems and impaired fertility.

Meanwhile, research by government and independent scientists has found that flame retardants provide no meaningful protection from furniture fires.

"Firemaster 550 was put on the market with almost no study," said Linda Birnbaum, director of the National Institute of Environmental Health Sciences, which funded the new research. "These findings are very preliminary, but what they found strongly suggests we need to follow this up with more research."

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